Schaff's Bible Dictionary
KNEE. Besides the literal use of the word, it is used figuratively. Taking children on the knees is adopting them. Gen 30:3; Jer 50:23. The knees were the seat of strength. Deut 28:35; Job 4:4; Isa 35:3; Nah 2:10; Heb 12:12. The head was put between the knees in abject supplication. 1 Kgs 18:42. Bending the knee is the simplest and most striking way of making or declaring one's self inferior to another, and thus it came to be used in prayer, worship, or humiliation. 2 Kgs 1:13; Isa 45:23; Dan 6:10-11; Luke 22:41; Rom 11:4; Eph 3:14; Phil 2:10; Acts 9:40; Acts 20:36.
The common Hebrew word for blessing is a form of the word translated "knee," and it is used for invoking God to bless, Gen 28:6; Josh 24:10; for invoking God for his blessing, Gen 12:3; Matt 18:18; for celebrating, praising, and adoring God, 2 Chr 6:13; Dan 6:11; for invoking blessings on others in the name of God. Ps 129:8; Gen 48:9; for God blessing his creatures. Gen 1:22; for emphatic greetings among men. 1 Sam 15:13:for invoking evil. 1 Kgs 21:10; Job 31:30.